Minced fish flesh is used for products such as fish balls and fish sausages. On an industrial scale minced fish is prepared either by mincing fillets or fish flesh obtained from beheaded and gutted fish from which the flesh has been separated from skin and bones in special separators whereby an increased yield of fish flesh is obtained. After cutting of fillets the remaining carcasses contain about 10 to 15 percent by weight of the total amount of the flesh and these can of course also be processed in the separating machines. Minced flesh from fillets has a comparatively good stability during frozen storage while fish mince prepared by utilization of skin and bone separators, hereinafter referred to as whole fish mince, from fish such as for example cod and haddock, has the disadvantage that it cannot be frozen and stored for later use without special treatment or without additives. This is due to the fact that some residues of the internal organs, such as kidney tissue, remain after gutting and these will be mixed into the minced fish flesh when skin and bone separators are used. Enzymes in these organs decompose trimethylamine oxide to formaldehyde, among other things. Formaldehyde reacts with fish protein, crosslinks the protein and changes its functional properties, such as its water-holding capacity, which in turn cause texture changes to such an extent that the minched fish flesh can e.g. not be used for the production of fish balls. This transformation of the protein is not prevented by freezing.
A number of chemical substances have been tried in order to improve the stability of minced fish during frozen storage. The objective has been to find chemical freezing stabilizers that do not cause changes of the taste, odor or texture of the minced fish. When used for whole fish mince they must prevent protein transformation for a long enough time that frozen storage is feasible. As examples of substances that have been tried as additives for freezing and storage can be mentioned polyphosphates, sorbitol, glycerol and amino acids. Of these substances only sugar and glycerols give freezing protection over a long period of time, but they have the disadvantage of conferring an undesirably sweet taste to the fish mince. Amino acids along give a bitter taste and attempts have been made to compensate this by using a combination of amino acids and sugars.